The present invention relates to circuit components mounted on circuit boards by solder column interconnects or arrays.
Advances in the electronics industry have created a demand for dense placement of electronic components on circuit boards. As a result, new technologies have been developed that allow circuit boards to accommodate an increasing number of components without becoming excessively large.
One such technology that is widely used is called flip-chip technology. Flip-chip technology includes area array technologies such the column grid array (CGA) technology. In flip-chip technologies, a semiconductor device, or integrated circuit (IC) package, having a pattern of conductive pads on a substrate, is joined face down to a circuit board or some other substrate.
A CGA IC package, for example, has a substrate with an array of solder columns that extend out from it, typically from the bottom surface. The substrate is typically composed of a ceramic material. Solder column interconnects or arrays are used to connect the IC package to the circuit board. The solder columns are attached at one end to connection pads or locations on the ceramic substrate. The solder columns are then soldered to respective pads on the circuit board using known techniques, such as a convection reflow solder process. The solder columns, therefore, establish interconnections that allow for electrical communication between the circuit board and the IC package.
The solder columns are of a sufficient height that, when an IC package is placed on a circuit board, the solder columns compensate for a coefficient of thermal expansion (CTE) mismatch. The CTE mismatch is the difference in the CTEs of the IC package and the circuit board and can produce stresses at the solder joints.
One problem with solder column arrays is that the solder columns do not withstand compressive force well. The solder columns are typically made of a 90%/10% Lead/Tin (Pb/Sn) solder, making them soft. Moreover, the individual solder columns are typically very thin. Consequently, if any significant amount of compressive force is applied to an IC package that is connected to a circuit board with a solder column array, the solder columns might, over time, compress and compromise the reliability of the IC package or circuit board.
Such compressive force could be the result of a cooling solution, such as a heat sink or fan, which is mounted on top of the IC package. In some instances, loads in excess of about 10 to 20 grams per solder column can exert sufficient compressive force to compromise reliability. Even without an attached cooling solution, the IC package itself might be too heavy for the solder columns to support without risk of solder column damage. Solder column damage such as solder column compression, bending, and breaking can result in shorting, IC package malfunction, or permanent destruction of the IC package or circuit board.
Cooling solutions often have considerable mass. It is not unusual for a cooling solution to exceed one pound. When large cooling solutions are exposed to shock and vibration that may be encountered during system operation, it is not uncommon to have thirty to forty pounds of force applied to the top of the IC package. This large load force can cause the solder columns to bend, deform, or break.
In addition to the large loads that could be present during shock and vibration, there is often a constant load of as much as 70 pounds applied to the cooling solution to maintain a good compressive force at the thermal interface between the cooling solution and the IC package. This constant compressive force could also cause significant column deformation over time.
One approach to minimize or eliminate solder column damage due to a load placed on a solder column array is to alleviate pressure exerted by a cooling solution that has been attached to an IC package by placing support columns between the circuit board and the attached cooling solution. However, this approach is obviously not applicable to IC packages that do not require the use of a cooling solution. The process of attaching the support columns also requires the undesirable use of some type of adhesive, such as an epoxy adhesive. Epoxy adhesives are not a preferred manufacturing solution because of handling and processing issues that are known in the art.
In one of many possible embodiment, the present invention provides a support assembly for supporting an integrated circuit package with an array of solder columns extending from a bottom surface of the integrated circuit package to a circuit board. The support assembly preferably includes a pair of shims for supporting the integrated circuit package, the shims being positioned along opposite edges of the integrated circuit package and placed between and abutting the integrated circuit package and the circuit board and a retention clip for aligning and securing in place the pair of shims.
Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims.